Method and apparatus for forming liquid alloys of alkali metals



Sept. 30, 1958 H. A. THOMAS METHOD AND APPARATUS FOR FORMING LIQUID ALLOYS OF ALKALI METALS Filed April 29, 1957 United States Patent METHOD AND APPARATUS FOR FORMING LIQUID ALLOYS 0F ALKALI NHETALS Henry A. Thomas, Baton Rouge, La., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware Application April 29, 1957, Serial No. 655,877

4 Claims. (Cl. 75-167) This invention relates to the manufacture of alloys of alkali metals and lead, especially sodium and lead. More particularly the invention relates to a new and improved method and apparatus whereby this valuable commercial intermediate alloy is efficiently and continuously made by a new and novel technique.

The alkali metal-lead alloys have been known and used for a number of years for various purposes, the predominating usage of such materials being in the manufacture of alkylated lead compounds. The foremost of these is tetraethyllead, which finds wide usage as an antiknock in the automotive fuel field. Through the years, various techniques have been developed and tried and commercially used for the preparation of such alloys, of which monosodium lead alloy, NaPb, is the most com mon example. One method of making such alloys was to cast molten alloy into large conical containers, after mixing up large batches of liquid alloy. Another method of making and blending alloy components involved the passage of sodium and lead through an extended conduit maintained at a specific temperature, and accompanying this operation with a weighing operation, in other words in following the correctness of mixing of the alloy components by the integrated specific gravity thereof. Such a process is disclosed in Wall Patent U. S. 2,723,913. Still another method of preparing molten alloy batches has involved. a stepwise process as is disclosed in Fisher et al. Patent 2,276,031. Inv the Fisher process, a portion of the: lead. to be found in the final alloy is charged to a manufacturing pot first, and. once this is done the remaining amount of lead and. all the sodium are charged, over a period of time, to final mixing of the entire batch. The purpose. of the initial lea'd portion in the Fischer eta al. process is to provide a substantial mass of metal as a type. of heat reservoir, since the alloying; process or the mixing of the alloy components is accompanied by not only the heat of physical mixing, but by a chemical reaction which involves substantial release of heat.

As far as is now known, there have been norsuccesstul commercially used continuous techniques for the manufacture of sodium lead alloy for various reasons. Thev Fischer et al batch. process: above referred to involves the preparation of very' large batches of the order of 100,000 pounds or thereabouts, and it is necessary to thoroughly mix the components after the additions of all the materials for a specific charge. This is done. to provide a homogeneous .melt and, of course, to permit taking arepresentative sample. Then, even after a sample is v provided for control analysis, even by the promptest delivery and analytical procedures, a .time lag of theorder of three fourths. of an hour to. several. hours is. always necessarily involved. It is thus: apparent, that the large quantity of alloywhich. has theoretically then beenprepared is merely held up as inventoryduring undesirable del-ay Accordingly, it. was highly desirable to have a. simple ice of sodium lead alloy or other alkali metal lead alloys, wherein the delivery or the product of the method would be of an assured precise and constant composition. Further it was desirable to have a process wherein the quantity of materials held up as processing inventory was minimized for obvious economic reasons. In addition apparatus was desired for continuous operation which would involve no important moving parts.

The objects of the present invention are, then, to provide generally a new and improved continuous process for the manufacture of alkali metals of lead. More specifically, an object of the present process is to provide a new and efficient process wherein a continuous stream of finished alloy, sodium-lead alloys being exemplary, is produced at a constant composition with the composition being actually controlled as a function of one of the process steps as will appear hereinafter. A further specific object is to provide a new and improved process which circumvents and avoids certain major disadvantages of previous batch operations, particularly insofar as heat effects arising from heats of reaction upon alloying are concerned. Yet another object is to provide a new and novel apparatus which is highly preferred for certain embodiments of the invention. Still another object of certain forms of the invention is to provide means whereby heat effects resultant from variations in production rates can be compensated for. Yet additional objects will appear hereinafter.

In the simplest and most general form of the process of the invention, a supply pool of molten lead is maintained, by appropriate addition of fresh lead, in a, usually, vertically extending primary zone. This primary supply pool, or lead zone surrounds at least in part a portion. of a second, vertically extended, reacting zone which, however, has considerable more elevation than the lead supply zone. Thus, the reacting zone extends from a feed point immersed within the lead supply zone to a level appreciably above the lead supply zone. This re,- acting zone is occupied by a vertically ascending mov' ing liquid column of sodium lead alloy, or in the lowermost portions thereof by the sodium and lead compoand. efiecti-ve. continuous technique for the preparation nentis in. the process of blending and mixing to form the desired alloy.

Entrance communication' to the above mentioned reacting zone is provided directly from the lead supply zone, the conduit providing the reaction zone having its lowermost opening in the lead supply zone. In addition a separate conduit is provided to introduce liquid sodium to the entrance to the reaction zone. The withdrawal of the completed alloy is at an elevated point in the react'ibn zone, the precise elevation being dictated by a number of factors as described hereinafter; as willbe discussed in more detail below, the vertical elevation of the point of withdrawal of alloy from the reaction zone setsf quite precisely the exact alloy composition produced for a given feed rate. There will be some very minor variation in composition when major changes in feed rate are desired but these can be readily avoided by' steps" hereafter described. By and large, of course, for commercial purposes, a specific installation is designed for a limited range of production cap'ac itiesand thus compensating adjustment is not. very frequently necessary. In certain additional mor'e specific forms of the process of the invention, the lead supply zone has a transverse area which is variable with height. In a preferred" modification: of such forms thelead supply pool includ es an upper portion having a large or extended: transverse area and a. lower. portion having a quite. small transverse area, both of these areas, however,,-being-. greater thanthe transverse area of the ascending. column, of. alloy. inpreparation. Yet another form Generally,v

3 of the invention is an explicit apparatus which utilizes to the highest degree the process variable of reacting mixture elevation above the lead supply pool as a control variable for constancyof composition of product. alloy.

The process of the present invention and a full understanding thereof will be most readily understood in conjunction with the accompanying figures and the follow ing example. The figures include Fig. 1 showing schematically a cross sectional elevation of an embodiment of the process. Fig. 2 is a similar schematic cross, sectional elevation view showing an embodiment wherein the process is rendered more stable by a subdivision of the lead supply pool into a lower portion of minor transverse area and an upper portion of relatively shallow depth but appreciably larger transverse area. Fig. 3 is a segmental illustration of a portion of the reaction zone in certain embodiments, wherein the path of the ascending product liquid alloy is altered to provide an acute angle to the horizontal, permitting particularly accurate control of, and constancy of, product alloy composition.

Generally, the process is applicable to substantially all the alloys of alkali metal and lead, and in the following examples, the mo-nosodium alloy of sodium and lead is used as exemplary for simplicity of illustration. It will be understood that alloys, for example, of potassium and lead or ternary alloys of potassium, sodium and lead are similarly readily processable.

Example I Referring to Fig. 1, apparatus and process streams of a process in operation are shown. The apparatus includes a main vessel 11, a reaction tube 12, a sodium supply line 13 and a discharge port or line 15. The vessels and conduits are suitably made of mild steel or certain cast ferrous alloys suitable for the service.

As an example of operation of the embodiment of Fig. l, a lead supply pool 16 of about 1000 parts of molten lead, generally at a temperature of about 400 to 450 C. is maintained therein, this lead supply pool surrounding the immersed portion of the reaction tube 12. In this specific embodiment the diameters of the lead supply pool vessel 11 and the reaction tube 12 are in the proportions of about 10:1, providing a transverse area ratio of 100:1. Fresh molten lead, in the proportions of about 10,000 parts per hour, and sodium, liquefied and at a temperature of somewhat above 212 F., say 220 F., is supplied to the process through a lead feed line 14, and a sodium feed line 13, respectively. As described below, in practice, sodium is fed at a rate suflicient to provide alloy at a desired production rate. The molten lead, fed through line 14, is merely fed at a rate suflicient to maintain a uniform level of the lead supply pool 16.

The position of the withdrawal tube 15 is at a level providing an elevation H above the level of the top surface 17 of the lead supply pool 16. In the course of operation, sodium and lead meet at the point or points of feed to the reaction tube 12 and immediately alloy in part,

forming a material whose composition is not important, 4

but which is'appreciably lighter in average density than the molten lead in the supply zone. This mixture rises in the reaction tube 12 and in the course of flow, complete mixing is obtained to yield a homogeneous, uniform composition alloy. It will be quite clear that the height to which the metal column in the reaction tube 12 attains above the level 17 of the lead supply pool 16 will be a function determined by the integrated weight of the liquid metal in the reaction tube 12 from the entry point 18 to the withdrawal point 15, as a hydraulic equivalent of the pressure head of the lead supply pool from the top level 17 thereof to the entrance 18 to the reactor tube 12. Thus, by appropriate positioning of the withdrawal line 15, the alloy which has risen to this point is of a pre-' cisely set composition of 10 percent sodium at thepoint 4 where H is equal to 0.9 the immersed length of the reaction zone in the lead supply pool. Typical dimensions are an immersion of 4 ft. of reaction tube 12 in the lead supply pool and an alloy head H of 43 inches.

The. composition of liquid alloy withdrawn from the reactor tube 12 at the discharge line 15 will remain essentially constant and precise during a wide range of production rates. However, there will be ordinarily some minor variation of composition if the proportions of production or the production rate is drastically changed. This arises from the fact that a higher production rate will cause a thicker or deeper withdrawal stream so that the mean elevation of the liquid alloy stream withdrawn under such circumstances will be slightly diiferent than when a very minor or modest rate of flow of alloy product stream is withdrawn. This minor variation is also readily compensated for by various adjustable positioning devices, a preferred example of which is discussed hereinafter. In the present example, the upward rate of flow in the reaction tube is at the rate of about 1.8 in. per second.

In the operation of this example, a continuous production of alloy of precise composition of the monosodium lead alloy, or 10 percent sodium content, is provided. In addition the lead supply pool is very easily maintained at the desired operating temperature of 400-450 C. owing to the substantial release of heat of reaction in the reaction tube 12, which is almost entirely transmitted directly to the lead supply pool and thence to the atmosphere or to a heat absorbing medium in a jacket (not shown) surrounding the lead supply pool.

In another preferred embodiment of the present proc ess, the advantage of a modest amount of lead metal inventory in processing is further emphasized by means discussed in the next example and illustrated in part by Fig. 2.

Example II Referring to Fig. 2, the apparatus for this embodiment is substantially the same as the apparatus used in Example I above, including a main supply vessel 23, a reaction tube 24, a sodium supply line 27, a lead supply line 26, and a discharge nozzle or port 25. The lead supply pool of the process, in contrast to Example I, however, includes a top zone 21 having an extended transverse area zone, and a lower zone 22, having only a relatively small transverse area. Typical proportions of the internal diameters of the reaction zone 24, the lower lead zone '22, and the top lead supply zone 21, are 1:3:9, corresponding to two transverse areas of 1:8:80, respectively. A further feature of the apparatus is that the relative vertical disposition of the reaction tube 24 and the lead supply vessel 23 can be varied, preferably by lowering or raising the vessel 23 by suitable adjustable support means. Typical support devices for adjustable positioning are hydraulic jacks 19 19, having reciprocatable rams or plungers 20 20 supporting the main lead supply vessel 23.

It will be quite apparent that when employing the same vertical elevations of the lead supply pool and the reaction zone as in Example I, that the quantity of molten lead held up as inventory in process is appreciably smaller, and may be of the order of from about 10 to 20 percent of the mass employed in Example I.

A further feature of the present embodiment, which is even more of a practical advantage, is the flexibility provided the process with respect to heat dissipating capacity. As already mentioned, in the formation of sodium lead alloy, a substantial amount of reaction heat is generated, the heat of reaction being 16,690 B. t. u. per pound mole of alloy, or 73 B. t. u. per pound. At a production rate of, for example, 1000 pounds of alloy per hour, then approximately 70,000 B. t. u. of process generated heat must be withdrawn. The apparatus of the present example provides adjustability to provide for heat release variability accompanying variations in production rate. As already mentioned, the relative vertical position of the reaction tube 124, with respect to the lead vessel 23, is adjustable. Hence, at high .production rat-es, the positionof 'the' lead vessel .is changed, by lowering, todecrease the portion thereof which is coextensive with, or surrounded by, the restricted crosssectional portion or zone "22 of the lead supply pool. Concurrently, the level of lead in the supply pool is increased, so that the head, H, of the discharge port '25 above the lead surface 29 is maintained constant. With such a revised position, the apparatus is capable of dissipating the increased amount of reaction heat accompanying an increased production rate.

While it is not intended to be restricted by any theoretical mode of explanation, it is believed that the :reason for the adaptability of the present example "to :maintaining thermal equilibrium for appreciably varying production rates, is as follows. The heat dissipated or removed from the process may be by transfer to a heat transfer medium in a jacket, not shown, surrounding the lead vessel. Alternatively, the heat may be discharged by radiation from the vessel exterior plus some convection to the atmosphere. It isfseen that the heat emanates from the reaction tube '24 and flows radially through the lead pool to the walls of the leadvesselizs for removal. When the reaction tube :is surrounded mostly by "the smaller lead zone 22, it is clear that the ultimate heat transfer surface, i. e., the vessel wall wetted by the lead supply pool, is relatively low. However, when the reaction tube is surrounded for a greater portion of its height by the lead :in the extended area zone 21, the heat transfer surface is greatly increased, and capacity is provided for discharging the heat generated. Jln all embodiments, the conductivity of the molten lead :is such that the. surfacetransfe'r area-is acontrolling factor.

From the foregoing, it will beseenthat the apparatus and process of Example 11 attends a tparticularlytsuitable embodiment of the invention wherein great latitude in production rates is permissible, and yet the objective of thermal stability is achieved.

An additional refinement in the process and apparatus therefor is illustrated by Fig. 3, which is a sectional, elevation view of the segmental extension of the reaction zone found in any embodiment of the process. As will be evident below, the extension may be regarded as a portion of the reaction zone.

Referring to Fig. 3, an upper portion 31 of a reaction zone is shown to which is attached an extension arm 32. The extension arm 32 is a conduit of approximately the same diameter as the reaction zone conduit 31, but is at an acute angle to the horizontal, usually of the order of 20 to 30 degrees. An aperture 33 is provided in the lower boundary of the extension arm 32, and slidably positioned adjacent the aperture 33 is a slide plate 34 having a smaller opening 35 therein. Guide means not shown are provided to maintain the slide plate 34 snugly against the outer surface of the extension arm 32.

A discharge chute 36 connects with the extension arm 32 to provide a closed passage for flow of alloy to subsequent storage or processing.

Means are provided for slidable positioning of the slide plate 34, said means including a protrusion 37 attached to the slide plate 34, and a threaded bar 38 attached thereto, the threaded bar passing through an extension 3? of the cover flange or cover plate 40 provided as a closure for the end of the extension arm 32. A hand wheel 41 engaging the threaded bar 38 provided for repositioning the slide plate 34 as desired.

During operation, liquid sodium lead alloy 42 rises through the upper portion 31 of a reaction tube and into the extension arm 32. As the level of the alloy adequately rises the alloy spills over the lower edge of the opening 35 in the slide plate 34. It will be readily apparcut that the discharge level of the alloyproductfcan be finely adjusted by adjustment of the position of the slide plate 34, owing to the angular position of the extension 32 with respect :to therhorizontal. This fine adjustment makes possible close and precise adjustment of the "discharge head with-minor variations :in process conditions, especially discharge temperature.

As heretofore stated, one of the particular beneficial features of the present process is the .fact that it permits .a stable thermal condition. By stable thermal conditions is meant that major variations of temperature .during time are minimized, thereby avoiding undue stresses in the apparatus. Heretofore, in batch operations, it has been necessary to not only supply heat during a portion of a cycle but'to extract copious quantities of heat during the portion of .a manufacturing cycle in which the exothermic reaction was being carried out. The present process avoids this tfluctuating thermal situation. Because of the continuing flow of alloy components in the reactor tube, a steady heat flux is achieved. In addition, inasmuch :as the heat generated by formation of the alloy is released at the center of the lead supply pool, or at :least at a position relatively remote from the boundaries thereof :as defined by atypical container vessel .11, .it :is quite apparent that the :heat flux through the lead supply pool is constant and from the interior rather than from :the exterior. This :highly advantageous situation :results in almost a total absence of heat shock or variable temperature'con'ditions imposed upon'the processing equipment. particular feature of the process can be utilized to a further extent :in that embodiments shown above achieve inherently or :by easy adjustment appropriate balance between heat supply to maintain the lead supply .puol inappropriate fluid condition, and the rate of processing desired. t

:It will be clear that numerous variations can be made in the details of the process without departing from the spirit thereof. Thus, it is ordinarily most effective to provide vertical disposition of the lead supply pool and of the reaction zone. It will be clear that the vertical alignment is not essential, and that for example, the reaction zone may be inclined if desired or necessary for equipment orientation. It is, of course, essential that the level of withdrawal of discharge or completed alloy from the reaction zone be at the appropriate or necessary elevation above the level of the lead in the supply pool.

Other variables which are important but not critical are the height of the lead supply pool, the immersion of the reaction zone within the supply pool and the extension of the reaction zone above the supply pool. Generally, it is highly desirable that a reaction zone length of at least a total of about 4 feet, and preferably about 6 feet be provided, to assure a. sufiiciently long traverse time to provide for homogeneous and thorough mingling of the product alloy. For higher capacity installations, a larger diameter reaction zone will be employed, and in such instances it is desirable to provide a somewhat longer reaction zone. Generally, a suitable guide for the proportions of the reaction zone is a lengthzinternal diameter ratio of about 20:1 to 40:1.

As is well known, alkali metals and alloys thereof are quite reactive and susceptible to deterioration upon contact with atmospheric moisture or oxygen. Hence, it is always essential that provision be made for blanketing the surfaces of the manufactured alloy, and desirably the lead, with an inert gas such as nitrogen or helium.

In the examples given above it will be clear that the extended transverse area proportions of the lead pool, particularly the upper surface thereof, is a process feature which renders control of the operation quite simple.

In practice, although a continuous stream of lead can suitably be provided, it will be frequently advantageous to merely intermittently add segmental increments of lead 7 thereof. If desired, suitable indicating devices, such as a two level probe system can be employed, for actuating signals or automatic feed arrangements. The sodium and lead supply lines are provided with appropriate control valves.

The benefit of insensitivity achieved by the extended transverse area of the lead pool upper level is similarly extended to the reaction zone by an enlargement of the upper portion thereof. For example, in Example II, an increase in diameter of the reaction zone in, suitably, the upper fifth thereof would provide a hold-up operation which would further simplify control of product compositions and assure constancy. It will be clear that the relative proportions of the lead supply pool transverse area and the reaction zone will vary primarily in degree in contributing to ease of control. However, in substantially all instances, it will be found quite desirable to provide a lead supply pool transverse area of at least-l times the transverse area of the reaction zone within the lead supply pool.

Having fully described the process and apparatus of the invention, what I claim is:

l. The continuous process for manufacture of an alkali-metal lead alloy comprising maintaining a supply pool of molten lead and a vertically extending reaction zone conduit having a lower opening immersed in the lead supply pool, and extending above the surface of the lead supply pool, feeding molten alkali metal to the said lower opening and concurrently admitting lead from the supply pool, thereby forming an ascending column of alkali metal-lead alloy in the reaction zone conduit, and withdrawing alloy therefrom at a point above the surface of the lead supply pool.

2. The process of'claim 1 further defined in that the surface of the lead supply pool is at least ten times the transverse area of the reaction zone within the supply pool.

3. A continuous process for manufacture of sodiumlead alloy comprising maintaining a vertically extending lead supply pool having a surmounting portion of relatively large transverse area and a lower portion of smaller transverse area, .and feeding liquid sodium to an opening at the bottom of a vertically extending reaction zone conduit, said conduit having a bottom portion surrounded by the supply pool and said opening being immersed in the lead supply pool, and admitting lead to the reaction zone conduit concurrently with the feed of sodium, thereby forming an ascending column of sodium lead alloy in the reaction zone conduit and withdrawing alloy therefrom at a point above the surface of the lead supply pool.

4. Apparatus for the continuous manufacture of sodium-lead alloy comprising a lead vessel for a lead supply pool, a reaction tube, a sodium supply conduit, a lead supply conduit, and adjustable support means for the lead vessel, the reaction tube being a vertically disposed conduit having a bottom opening and a top discharge port and being positioned with the bottom opening and a lower portion of the conduit within the confines of the lead vessel, the lead vessel having a vertically variable transverse area increasing toward the top thereof, the support means being adapted to alter the elevation of the lead vessel with respect to the reaction tube, whereby a constant lower portion of the reaction tube can be surrounded by a lead pool having a variable boundary surface.

References Cited in the file of this patent UNITED STATES PATENTS 380,524 Schlapp Apr. 3, 1888 2,091,801 Amick et al. Aug. 31, 1937 2,158,517 McParlin May 16, 1939 2,276,031 Fisher et al Mar. 10, 1942 2,549,790 Finkeldey et al. Apr. 24, 1951 2,723,913 Wall Nov. 15, 1955 2,728,656 Neher Dec. 27, 1955 

3. A CONTINUOUS PROCESS FOR MANUFACTURE OF SODIUMLEAD ALLOY COMPRISING MAINTAINING A VERTICALLY EXTENDING LEAD SUPPLY POOL HAVING A SURMOUNTING PORTION OF RELATIVELY LARGE TRANSVERSE AREA AND A LOWER PORTION OF SMALLER TRANSVERSE AREA, AND FEEDING LIQUID SODIUM TO AN OPENING AT THE BOTTOM OF A VERTICALLY EXTENDING REACTION ZONE CONDUIT, SAID CONDUIT HAVING A BOTTOM PORTION SURROUNDED BY THE SUPPLY POOL AND SAID OPENING BEING IMMERSED IN THE LEAD SUPPLY POOL, AND ADMITTING LEAD TO THE REACTION ZONE CONDUIT CONCURRENTLY WITH THE FEED OF SODIUM, THEREBY FORMING AN ASCENDING COLUMN OF SODIUM LEAD ALLOY IN THE REACTION ZONE CONDUIT AND WITHDRAWING ALLOY THEREFROM AT A POINT ABOVE THE SURFACE OF THE LEAD SUPPLY POOL. 